Han-Yueh Kuo

Clonal spread of multidrug-resistant Acinetobacter baumannii in eastern Taiwan

BACKGROUND AND PURPOSE This study was conducted to investigate the molecular epidemiology and antimicrobial susceptibility of multidrug-resistant (MDR) Acinetobacter baumannii to three types of antibiotics. METHODS One hundred and thirty-four specimens of MDR A baumannii were collected from three branches (Taipei, Dalin, and Hualien branches) of Buddhist Tzu Chi Hospital, which are located in northern, southern, and eastern Taiwan, during 2007. Genotyping was performed by pulsed-field gel electrophoresis. Antibiotic susceptibilities to colistin, rifampicin, and tigecycline were determined. The synergistic effects of rifampin and colistin were also evaluated. RESULTS Antibiotic susceptibility testing showed that 10.4%, 47.8% and 45.5% of the MDR A baumannii isolates are resistant to colistin, rifampicin, and tigecycline, respectively. A majority of the rifampicin-resistant isolates (62.7%) were found in the Haulien branch, whereas 62.2% of tigecycline-resistant isolates were found in the Taipei branch. The combination of colistin and rifampicin had a synergistic effect on all of the isolates. Genotyping by pulsed-field gel electrophoresis identified 17, 23, and 11 pulsotypes in the Taipei, Dalin, and Haulien branches, respectively. Furthermore, 74.5% of isolates in the Haulien branch were identified as one of three pulsotypes. Among 37 rifampicin-resistant and 22 tigecycline-resistant MDR A baumannii isolates found in the Haulien branch, 51.3% (19/37) and 50% (11/22) of the isolates belonged to the same clone, respectively. CONCLUSION This study confirms the high prevalence of resistance to rifampicin and tigecycline in MDR A baumannii in the three hospitals that were studied, and the high proportion of identical strains that exist in eastern Taiwan.

Imipenem: a potent inducer of multidrug resistance in Acinetobacter baumannii

This study investigated the progression of multidrug resistance upon exposure to imipenem in Acinetobacter baumannii. Eighteen A. baumannii strains, including two reference strains (ATCC 19606 and ATCC 17978), four clinical strains (AB56, AB242, AB273 and AB279) and 12 antibiotic-selected mutant strains, were used in this study. Imipenem-selected mutants were generated from imipenem-susceptible strains (ATCC 19606, ATCC 17978 and AB242) by multistep selection resistance. Amikacin-, ciprofloxacin-, colistin-, meropenem- and ceftazidime-selected mutants were also generated from the two reference strains and were used for comparison. Antibiotic susceptibilities in the absence and presence of the efflux pump inhibitors carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 1-(1-naphthylmethyl)-piperazine (NMP) were examined in the three imipenem-selected mutants and the three clinical multidrug-resistant (MDR) isolates. Expression profiles of the antimicrobial resistance genes in the imipenem-selected mutants and their parental strains were also determined. The results showed that imipenem was more likely, compared with the other antibiotics, to induce a MDR phenotype in the two reference strains. Differences in OXA-51-like carbapenemase, efflux pumps or/and AmpC β-lactamase expression were observed in the three imipenem-selected mutants. Moreover, a reduction in imipenem or amikacin resistance was observed when the imipenem-selected mutants and clinical isolates were exposed to NMP and CCCP. This study concluded that imipenem might be a potent inducer of multidrug resistance in A. baumannii strains. OXA-51-like carbapenemase combined with other resistance mechanisms may contribute to the development of multidrug resistance in A. baumannii. Monitoring the use of carbapenems is required to reduce the spread of MDR A. baumannii in hospitals.

The sensor kinase BfmS mediates virulence in Acinetobacter baumannii

BACKGROUND/PURPOSE BfmR, the response regulator component of the two-component system BfmRS, has important roles in biofilm formation and cellular morphology of Acinetobacter baumannii. Until now, the contribution of the sensor kinase BfmS to the virulence of this bacterium remains unknown. In this study, a bfmS knockout and complementation studies were performed to clarify the role of BfmS in A. baumannii virulence. METHODS We constructed a bfmS knockout mutant in the A. baumannii 17978 type strain by transposon inactivation. To clarify the role of bfmS in A. baumannii virulence, the biofilm formation, adherence ability to eukaryotic cells, serum resistance, and antibiotic susceptibility tests were performed in A. baumannii 17978 and its derivative knockout and complementation strains. RESULTS The bfmS knockout displayed a reduction in biofilm formation, loss of adherence to eukaryotic cells, and greater sensitivity to serum killing compared with the parent strain. Proteomic analysis of culture supernatants revealed that the release of outer membrane proteins (Omps), including CarO and outer membrane protein A (OmpA), was associated with the inactivation of BfmS in A. baumannii. CONCLUSION This study is the first to demonstrate that the pathway regulated by the sensor kinase BfmS is associated with biofilm formation, adherence to biotic surfaces, serum resistance, and antibiotic susceptibility, which may be associated with the release of Omps in A. baumannii.

Distribution of blaOXA-carrying imipenem-resistant Acinetobacter spp. in 3 hospitals in Taiwan.

We investigated the molecular epidemiology and OXA-type carbapenemase genes of 83 imipenem-resistant Acinetobacter spp. collected from 2 university hospitals (hospitals A and B) and a regional hospital (hospital C) during 2007 in Taiwan. Genotyping by pulsed-field gel electrophoresis identified 51 pulsotypes. None of the pulsotypes established predominance throughout the 3 hospitals. Multiplex polymerase chain reaction of blaOXA genes showed that 100% (18/18), 91%(31/34), and 100% (31/31) of the Acinetobacter spp. collected from hospital A, B, and C, respectively, possessed blaOXA-51-like genes. None of the strains carrying blaOXA-23-like and blaOXA-24-like genes were found in hospital A. The coexistences of blaOXA-51-like/blaOXA-23-like and blaOXA-51-like/blaOXA-24-like genes detected in hospitals B and C were 26% (9/34) and 12% (4/34) and 58% (18/31) and 3% (1/31), respectively. Among blaOXA-23-like gene-carrying isolates collected from hospitals, clonal spread of strains carrying the blaOXA-23 gene was detected in the regional hospital but not the other 2 university hospitals. The results suggest that interhospital dissemination of imipenem-resistant Acinetobacter spp. was not found in these hospitals. The increasing percentage of OXA-23 in OXA-type carbapenemases in Acinetobacter spp. from the regional hospitals to medical centers deserves further attention in Taiwan.

The origin of Acinetobacter baumannii TYTH-1: a comparative genomics study

There have been increasing reports of bla(OXA-23)-carrying strains of carbapenem-resistant Acinetobacter baumannii (CRAB), which has become a significant public health concern in Taiwan. To determine the origin of these CRAB strains, the prevalence of CRAB and bla(OXA-23)-carrying CRAB in a regional hospital was analysed retrospectively. The genome of A. baumannii TYTH-1 was completely sequenced and annotated. Multiple comparative genomics studies, including phylogenetic analysis, functional comparison via the Clusters of Orthologous Groups (COGs) database, and determination of variance in GC profiles in the whole genome and gene arrangements in resistance islands, were performed using 11 completely sequenced A. baumannii genomes. bla(OXA-23)-carrying CRAB isolates became dominant clones in 2007. A comparative genomics analysis revealed a common strain lineage between Taiwanese strains (TYTH-1 and TCDC-AB0715) and Chinese strains (MDR-TJ and MDR-ZJ06). Phylogenetic studies and GC profiles showed that the genome of TYTH-1 was closest to MDR-ZJ06. However, the resistance island of TYTH-1 (RI(TYTH-1)) was nearly identical to that of RI(MDT-TJ). The functional category for COGs was similar in the tested genomes. The results reveal that dissemination of bla(OXA-23)-carrying CRAB in Taiwan may have been mediated by the transfer of people between Taiwan and China during 2007. The global spread of CRAB is now a worldwide public health problem. In Taiwan, the government needs to focus more attention on the importance of identifying and tracing resistant pathogens and issuing notifications of CRAB infections.

Emergence and dissemination of blaOXA-23-carrying imipenem-resistant Acinetobacter sp in a regional hospital in Taiwan

BACKGROUND The distribution and characterization of OXA-type carbapenemases in Acinetobacter sp in Taiwan has less been reported. The aim of the study was to investigate the molecular epidemiology and OXA-type carbapenemase genes in a regional hospital in Taiwan. METHODS Imipenem-resistant Acinetobacter sp were collected between 2005 and 2007 in a regional hospital. Genotyping was performed by pulsed-field gel electrophoresis. OXA-type carbapenemase genes were determined by multiplex polymerase chain reaction (PCR) and gene sequencing. RESULTS A total of 136 isolates were collected. Fifty-six pulsotypes were identified. None of the pulsotypes established predominance throughout the 3-year period. Multiplex PCR of blaOXA genes showed that 99% (135/136) of the Acinetobacter sp possessed blaOXA51-like genes. The coexistences of blaOXA51-like/blaOXA-23-like and blaOXA51-like/blaOXA-24-like were detected in 19% (26/136) and 1% (2/136) of the isolates, respectively. Among blaOXA-23-like gene-carrying isolates, two isolates (Pulsotypes 18 and 20) were found in 2006 and the remainder (n=24), including Pulsotypes 27 (n=18), 29 (n=1), 52 (n=3), and 53 (n=2), were found in 2007. Sequencing performed on the 26 representative isolates confirmed the presence of the blaOXA-23 carbapenemase gene. Analysis of the genetic content of blaOXA-23 showed that these genes were presumably chromosomal and associated with the upstream-located insertion sequence ISAba1. CONCLUSIONS The emergence and imminent widespread of blaOXA-23-carrying imipenem-resistant Acinetobacter sp appeared in Taiwan during the period from 2006 to 2007.

Genome Sequence of Acinetobacter baumannii TYTH-1

Acinetobacter baumannii has emerged recently as a major cause of health care-associated infections due to the extent of its antimicrobial resistance and its propensity to cause large nosocomial outbreaks. Here we report the genome sequence of Acinetobacter baumannii TYTH-1 isolated in Taiwan during 2008.

Risk factors for levofloxacin resistance in Stenotrophomonas maltophilia from respiratory tract in a regional hospital

OBJECTIVES Stenotrophomonas maltophilia is a bacterial pathogen associated with health-care associated infections, particularly in immunocompromised patients. Members of the fluoroquinolone drug class are frequently used to treat S. maltophilia infection; however, S. maltophilia resistance to fluoroquinolones, especially levofloxacin, has been increasing. METHODS We sought to identify risk factors associated with levofloxacin resistance using a case-control study. We examined sputum from 76 S. maltophilia-positive patients admitted to our hospital between January 1, 2010 and June 30, 2011. Case groups were defined as patients who had S. maltophilia infections resistant to levofloxacin, and control groups were defined as patients who had S. maltophilia infections susceptible to levofloxacin treatment. Patient information including demographics, previous antibiotic use, and other traits were recorded. In addition, S. maltophilia isolates from patient sputum were assessed for antibiotic resistance as well as for the presence of genes associated with drug resistance. RESULTS Previous antibiotic treatment with first- or second-generation cephalosporin was found more often in the levofloxacin-susceptible group; by contrast, previous piperacillin/tazobactam treatment occurred more often in the levofloxacin-resistant group. Three genes associated with drug resistance, including SmeA, SmeD, and SpgM were not significantly different between these groups. CONCLUSION Piperacillin/tazobactam treatment is associated with subsequent isolation of levofloxacin-resistant S. maltophilia from the respiratory tract.

Prevalence and mapping of a plasmid encoding a type IV secretion system in Acinetobacter baumannii

We investigated the prevalence of a type IV secretion system (T4SS)-bearing plasmid among clinical isolates of carbapenem-resistant Acinetobacter baumannii (CRAB) using plasmid replicon typing. The complete sequence of a T4SS-bearing plasmid, pAB_CC, isolated from A. baumannii TYTH-1 was determined, and a comparative analysis of the T4SS gene modules was performed. Of the 129 isolates studied, GR6 (repAci6) was the most common (45 of 96 isolates) and was strongly linked with the T4SS. A comparative analysis of the T4SS locus in seven plasmid genomes, including pAB_CC, pACICU2, pABKp1, pABTJ1, p1BJAB0714, p2BJAB0868, and p2ABTCDC0715, indicated that fourteen genes on these plasmids were highly conserved compared to those of the F plasmid. Additionally, the chromosomes in the seven representative isolates may be evolutionarily distinct from their intrinsic T4SS-bearing plasmids, suggesting that the two T4SS lineages emerged long before the appearance of EC II. These two lineages are now widespread in A. baumannii strains.

A comparative study of class 1 integrons in Acinetobacter baumannii.

Multidrug resistance (MDR) in Acinetobacter baumannii is increasingly reported and has become a significant public concern. The method responsible for the acquisition of resistance genes via integrons from the environment or intra-species in A. baumannii remains to be understood. This study was performed to investigate the transmission route of these integrons using a comparative analysis of published A. baumannii complete genomes. The phylogenetic analysis of A. baumannii type 1 integrases (IntI1) showed that the integrons could be transferred across the two evolutionary lineages, the international clone I (IC I) and clone II (IC II) strains. In addition, the integrons in A. baumannii strains were mainly responsible for the transfer of resistance genes for two types of long-term usage antibiotics and antiseptics, such as aminoglycosides, chloramphenicol and the quaternary-ammonium-compound family. The in silico comparative analysis of known integron integrases revealed that the intI genes were phylogenetically related among A. baumannii strains and some microorganisms living in a sediment community, implicating that the integrons of A. baumannii might have originated from those microorganisms belonging to the β-preoteobacterial class in the sediment environment. The data suggest that the gain of class 1 integrons in A. baumannii strains may have started before the antibiotic era. This report shows that the origins of A. baumannii class 1 integrons may be the soil environment and that the resistance genes included in integrons are horizontally transferred across all the A. baumannii genomes, including IC I and IC II.